ME 114 – Engineering Drawing II
GEAR DRAWING
Mechanical Engineering
University of Gaziantep
Oğuzhan YILMAZ PhD
Associate Professor
Gear Types
 A gear is a toothed wheel which is used to transmit power and motion between machine parts.
 Gears are used in many applications like automobile engines, household appliances, industrial machine tools.
 When two gears of different sizes are meshed , the larger is called “gear” while the smaller is “pinion”.
 A gear train is combination of two or more gears to change the speed or direction of motion of shaft systems.
Straight Bevel Gears
Spur Gears
Helical Gears
Herringbone Gear
Worm and Gear
Hypoid Gears
Spiral Bevel Gears
Planetary Gears
Rack & Pinion
1
Gear Tooth Terminology
Root Diameter : Diameter of root circle
Pitch Diameter : Diameter of imaginary pitch circle specifying
addendum and dedendum
Outside Diameter : Diameter of addendum (outside) circle
Addendum : Radial distance from pitch to top of tooth
Dedendum : Radial distance from pitch to bottom of tooth
Circular Pitch : Distance on pitch circle from a point on one tooth
to corresponding point on the adjacent tooth
Tooth Thickness : Thickness of a tooth along the pitch circle
Clearance : Distance between top of a tooth and bottom
of mating space
Working Depth : Distance a tooth projects into mating space
Whole Depth: Total height of the tooth
2
Involute Gear Profile
 The standard gear profile in an involute that keeps the meshing
gears in contact as the gear teeth are revolved.
 The method of constructing an involute is illustrated.
 Step 1: A base arc having the center of base circle is drawn
and divided into equal divisions with radial lines from the center
of arc. Tangents are drawn perpendicular to these radial lines
at the points where they intersect the base arc.
 Step 2: The chordal distance from point 1 to point 0 is used as
a radius with point 1 as the center. This distance is revolved to
find point 1 on the involute. Then, the distance from point 2 to
the newly found point 1 is revolved to the line tangent to the arc
through point 2 to give point 2 on the involute. This procedure
is followed until the complete involute curve is obtained.
 It is unnecessary to follow this procedure to draw gear teeth
since most detail gear drawings employ approximations of gear
teeth. Gear teeth are actually not shown on technical drawings;
instead conventional methods of specifying them are used with
notes and tables.
3
Gear Meshing
 Meshing of two spur gears with a center distance is shown below.
 The line of action (also known as “pressure line”) is a line drawn
tangent to the base circle of pinion and gear.
 When two gear teeth are in contact, the kinematic principle of
gearing is demonstrated: the angular velocity ratio of the meshing
gears is constant along the line of action.
 The pressure angle is the angle between the tangent to the pitch
circles and the line of action.
 Gear catalogs are classified according to the number of teeth and
the pressure angle.
Line of Action
4
Detail Drawing of Gears
Spur
gears
Bevel
gears
Rack and Pinion
Worm and Gear
5
Equations for Cylindrical Spur Gears
Module (Modül) :
Pitch (Adım) :
Outside Dia. (Diş Üstü Çap) :
m
D
p Dp

 0

z
z 2
p  m
 Dp
z

D0
z 2
D0  Dp  2m  mz  2
Pitch Dia. (Bölüm Dairesi Çapı) : Dp  m z  D0 - 2m
Root Dia. (Diş Dibi Çap) : Dr  D0 - 2h  Dp - 2b
1
a

m

Addendum (Diş Üstü Yükseklik) :
h
Dedendum (Diş Dibi Yükseklik) : b 1.25m
Whole Depth (Diş Yüksekliği) : h  b  a  2.166m 
13
m
6
Clearance (Diş Boşluğu) : c  b - a  0.166m
Center Distance (Merkezler Arası Uzaklık) : e 
Gear Ratio (Dişli Oranı) :
D p1  D p2
2
 z z 
 m 1 2 
 2 
n1 z 2

n2 z1
z : # of Teeth (Diş Sayısı) Face Width: 3p < F < 5p
α : Pressure Angle (Kavrama Açısı) = 15º - 20º (according to DIN 867)
6
Gear Bodies
 There are various types of gear bodies used
in industry. They are preferred according to
their purpose of use (such as light gears by
removing excessive material, strengthened
gear bodies using stiffeners, etc.)
Webbed
Blank
Gear
Stiffener
Pulley
Gear
Webbed
with
Cores
Spoked
7
Two-views of a spur gear
The drawing of a gear should be consisting of all technical details.
The drawing must shown the details of the gear, the hub, web and other features.
8
Two-views of a spur gear
Outside Dia.
Pitch Dia.
Root Dia.
9
Drawing of mating spur gears
•Draw front and sectioned side view of the spur gear pair.
•Calculate the other necessary data to draw the gear pair.
•Fully dimension the object.
•Place the cutting data on your drawing.
CUTTING DATA
Module (mm)
Number of teeth
Rotational speed (rpm)
Face width (mm)
Shaft diameter (mm)
Hub diameter (mm)
Hub thickness (mm) (single sided)
Keyway (mm)
Number of holes
Center diameter of holes
Material
Pinion
12
?
1600
?
50
100
100
4x4
----AISI 4340
Gear
?
30
960
?
100
165
120
6x6
6 x Ø40
123
Cast Iron
10
11